1. Field of the Invention
The present invention pertains to ground penetrating radar (GPR) data acquisition and more particularly to acquiring ground penetrating radar data through the use of seismic data acquisition technology to obtain more accurate relative amplitude information.
2. Related Prior Art
Prior art has demonstrated many methods for using various types of generated electromagnetic waves to penetrate the earth's surface. Many of these contain methods and apparatus for receiving the reflected waves and obtaining limited information. The most prevalent use of waves of the nature of radar are to locate solid objects that are located at some point below the surface. However, prior art has provided some insights into the use of radar to locate subsurface anomalies. The following patents are relevant in their illustration of the use of electromagnetic waves to acquire subsurface information.
U.S. Pat. No. 3,967,282, "Underground Pipe Detector", (Young, et. al.), relates to an apparatus and method wherein an electrical impulse source transmits a radar type signal through an antenna into the ground and is reflected by a target. The reflected signal or echo is detected by the antenna and an analog to digital converter converts it to a digital form which may be readily operated on, stored and recalled. A memory stores the information until recalled for comparison with a subsequent signal. A processing means compares the stored and subsequent signal to give an indication of the location of metallic and non-metallic buried targets.
U.S. Pat. No. 4,008,469, "Signal Processing in Short-Pulse Geophysical Radar System", (Chapman), relates to signal processing techniques and apparatus for use in short pulse geophysical radar systems to improve signal to noise ratio, reduce r.f. interference, improve resolution, and reduce ambiguities.
U.S. Pat. No. 4,218,678, "Synthetic Pulse Radar Including A Microprocessor Based Controller", (Fowler, et al.), relates to pulse radar detection of targets in extended media, including natural phenomena such as oil, coal, and ore deposits within the earth. In particular, this invention relates to a pulse radar system employing a synthetic pulse formed from a Fourier spectrum of frequencies generated and detected by a digitally controlled transmitter and receiver circuits.
U.S. Pat. No. 4,245,191, "Method and Apparatus for Detecting and Measuring Inclusions in Subsoil", (Schroeder), relates to a method and apparatus comprising a transmitter for transmitting an unmodulated carrier of selected wave length into the ground and a receiver adapted to receive reflected signals. Circuitry is described for producing narrow pulses from the transmitted and received signals for displaying them on an oscilloscope and on a plotter. The display on the oscilloscope is rotated through ninety degrees from the conventional display so that the pulses corresponding to the transmitted and reflected signals appear as horizontal bars spaced apart vertically by distances which correspond to the depth of the inclusions below the surface. The wave length is selected to be at least four times the anticipated depth of the inclusions.
The apparatus is described as being incorporated into a motor vehicle such as a Land Rover with the transmitting antenna mounted at the front and receiving antenna at the rear of the vehicle. The apparatus is most conveniently situated in place of the co-driver's seat for operation by an operator sitting in the rear of the vehicle. Decoupling between transmitting and receiving antennae is partially achieved due to the rotation through ninety degrees of the polarity of the reflected wave relative to the transmitted wave.
U.S. Pat. No. 4,258,321, "Radio Geophysical Surveying Method and Apparatus", (Neale), relates to a method and apparatus for radio geophysical surveying and includes measuring the relative magnitude and phase of radio frequency signal components reflected from subterranean formations. The apparatus comprises a transmitter selectively connected to a vertical antenna and a loop antenna. Also included is a pair of receivers, one receiver being connected to a vertical antenna and the other to a loop antenna. A surface propagated calibration signal is transmitted and is received by each of the receivers. The outputs of the receivers are connected to the input of a difference amplifier, a difference signal is generated, and the magnitude and phase of the difference signal are measured and recorded. A survey signal, including surface propagated components and earth propagated components, is then transmitted. The survey signal is received, a difference signal is generated, and the magnitude and phase thereof are measured. For each position along the survey path, the calibration magnitude and phase are vectorially subtracted form the corresponding survey magnitude and phase, and the resultant magnitude and phase are plotted. At each position, the data is taken for an electric field vector alignment of the transmitter and receiver loop antennas, and for a magnetic field vector alignment thereof. The transmitter and receivers include means for precisely maintaining consistency throughout the survey.
U.S. Pat. No. 4,430,653, "Earth Probing Radar System", (Coon, et al.), relates to a ground probing radar method and apparatus which is used to view the earth in advance of coal mining activity and provides visual display of a coal seam and particular discontinuities that may lie therein. The system operates in the frequency range of 10 Megahertz to 5 Gigahertz. The received electromagnetic energy is amplified, sampled and band pass filtered with subsequent time gain amplification. A time analog return signal may be viewed directly and/or the return signal may be digitally processed to enable further signal refinement. A control microprocessor is utilized for both tape record control and digital signal processing. The processor includes the capability for compositing and/or stacking of common source point data for output record and display.
U.S. Pat. No. 4,504,833, "Synthetic Pulse Radar System and Method", (Fowler, et al.), relates to a method and apparatus for detecting geophysical phenomena by the use of a synthetic pulse radar. A radar transmitter generates a plurality of component signals of different frequencies which approximate at least a portion of the Fourier transform of a radar short pulse. These component signals are transmitted simultaneously for modulation by the geophysical phenomena, and the modulated component signals are substantially simultaneously received in a receiver. The receiver divides the components signals, and as to each determines representative parameters. This patent also includes a heterodyne receiver which operates with a fixed IF frequency and incorporates a single frequency quadrature system.
U.S. Pat. No. 4,544,892, "Signal Processing Apparatus for Frequency Domain Geophysical Electromagnetic Surveying System", (Kaufman, et al.), relates to a frequency domain geophysical electromagnetic surveying system in which intermittent primary fields having sharp terminations are generated in a cycle having a fundamental frequency by a transmitter. A receiver includes a gate passing only secondary signals received during interruptions of the primary field, the gated signal being applied to filters tuned to harmonics of the predetermined frequency. The filter outputs are synchronously demodulated to provide signals corresponding to at least the in phase component of the secondary signal at the fundamental frequency, and preferably in phase and quadrature components of at least two harmonics.